Silicon carbide and other films and method of deposition

ABSTRACT

A method of depositing a ceramic film, particularly a silicon carbide film, on a substrate is disclosed in which the residual stress, residual stress gradient, and resistivity are controlled. Also disclosed are substrates having a deposited film with these controlled properties and devices, particularly MEMS and NEMS devices, having substrates with films having these properties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

A part of this invention was made with government support underContracts No. NCA3-201 awarded by NASA and DABT 63-1-0010 awarded byDARPA. The government has certain rights in this invention.

BACKGROUND

The present invention relates to silicon carbide and other films, and,more particularly, to controlled deposition of these films on asubstrate.

Semiconductor, micro- and nanoelectromechanical systems (MEMS/NEMS)apply integrated circuit fabrication technology to fabricate optical,mechanical, electrochemical, and biosensor devices. One of the importantsteps in creating MEMS and NEMS devices is the deposition of thin filmsof material onto substrates. Once the films are deposited, variousetching techniques may be employed to shape the deposited film.

In typical MEMS/NEMS devices, silicon is a primary material. Siliconcarbide is a material that has very good physical and chemicalcharacteristics, and is noted for these properties at temperatures aboveabout 300° C. Silicon carbide is an advantageous material for use infilms for MEMS and NEMS, particularly because of its exceptionalelectrical, mechanical, and chemical properties compared to silicon innormal and harsh operating environments.

One of the barriers limiting development of silicon carbide in MEMSproduction has been the inability to deposit uniform films of siliconcarbide on large area substrates having properties that are advantageousto and required for MEMS and NEMS. Deposition of silicon carbide isconventionally subject to variations in residual stress, residual stressgradient, and electrical resistivity. These properties are important tothe proper operation of MEMS and NEMS devices.

With silicon, residual stress, residual stress gradient and electricalresistivity can be controlled after the film is deposited by annealingthe film at elevated temperatures. Annealing in silicon inducescrystallographic changes that result in the modification of theseproperties. With single crystalline and polycrystalline silicon carbide,such an approach is not feasible because silicon carbide is chemicallyand crystallographically stable at conventional annealing temperatures.For silicon carbide films deposited on silicon substrates, annealing iscompletely ineffective because the non-silicon carbide substrate limitsthe annealing temperatures to temperatures too low for effectiveannealing. The present invention bypasses the need for annealingaltogether by implementing control of the residual stress, residualstress gradient, and electrical resistivity in the silicon carbide filmsduring the film formation (deposition) process.

SUMMARY OF THE INVENTION

The present invention provides methods of depositing films on asubstrate that enables control of the residual stress, residual stressgradient, and electrical resistivity of the deposited film. Theinvention includes films of various compositions, such as ceramic filmswith the ceramic compound having a metallic and non-metallic component.Preferably, the film is a silicon carbide film. The silicon carbide filmis deposited by chemical vapor deposition onto a substrate, such as asilicon substrate, by placing the substrate in a reaction chamber andevacuating the chamber to a pressure below about 10 mtorr. Thetemperature of the chamber is maintained at about 900° C. A carbonprecursor, such as acetylene (5% in hydrogen) is supplied to the chamberat a flow rate of about 180 standard cubic centimeters per minute(sccm). A silicon precursor, such as dichlorosilane (DCS), is suppliedto the chamber at a flow rate of about 54 sccm. As the precursors aresupplied, the pressure of the reaction chamber increases and may bemaintained at a fixed pressure.

Under these conditions, tensile films with appreciable stress gradientsare deposited at pressures less than 2.65 torr and compressive filmswith appreciable stress gradients are deposited at pressures greaterthan 2.65 torr. At 2.65 torr, the film has a very low residual tensilestress (<20 MPa), a negligible stress gradient, and a resistivity thatis less than 10 Ω·cm without intentional doping. So control of thepressure with other parameters fixed resulted in control of the residualtensile stress, stress gradient, and electrical resistivity.

In another embodiment, the chamber is maintained at a pressure of about2.0 torr. A carbon precursor, such as acetylene (5% in hydrogen), issupplied to the chamber at a flow rate of about 180 standard cubiccentimeters per minute (sccm). A silicon precursor, such as DCS, issupplied to the chamber at a flow rates between 18 and 72 sccm. Underthese conditions, tensile films with appreciable stress gradients aredeposited at DCS flow rates below 35 sccm and compressive films withappreciable stress gradients are deposited at DCS flow rates above 35sccm. At a DCS flow rate of 35 sccm, the film has a very low residualtensile stress (<20 MPa), a negligible stress gradient and a resistivitythat is less than 10 Ω·cm without intentional doping. So control of theflow rate of the metal element precursor, in this case the siliconprecursor DCS, with other parameters fixed resulted in control of theresidual tensile stress, stress gradient, and electrical resistivity.

The present invention also relates to substrates having a siliconcarbide film deposited thereon in which the residual stress is 0±100 MPaand the achieved electrical resistivity is less than about 10 Ω·cm, andto semiconductor, MEMS, and NEMS devices having such substrates.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus used in the presentinvention;

FIG. 2 is a schematic view of another embodiment of an apparatus used inthe present invention;

FIG. 3 is a graph of residual stress versus pressure for one embodimentof the present invention;

FIG. 4( a) is a SEM micrograph of a silicon carbide cantilever from afilm made in accordance with one embodiment of the present invention;

FIG. 4( b) is another SEM micrograph of a silicon carbide cantileverfrom a film made in accordance with one embodiment of the presentinvention;

FIG. 5 is a graph of electrical resistivity versus deposition pressurefor one embodiment of the present invention;

FIG. 6 is a graph of residual stress versus dischlorosilane flow ratefor one embodiment of the present invention;

FIG. 7 is a SEM micrograph of a silicon carbide cantilever from a filmmade in accordance with one embodiment of the present invention; and

FIG. 8 is a graph of electrical resistivity versus dischlorosilane flowrate for one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to the deposition of film, preferably asilicon carbide (SiC) film, onto a substrate with control of variousproperties, such as residual stress, residual stress gradient, andelectrical resistivity. The invention will be described as it relates todeposition of SiC onto a silicon substrate, particularly for use withMEMS and NEMS devices. The invention, however, is only exemplified bysuch description and is limited only by the claims included herein.

Silicon carbide film, particularly polycrystalline SiC film, isdesirable for use in MEMS and NEMS devices, as described above. Controlof key properties, such as residual tensile stress, residual tensilestress gradient, and electrical resistivity, provides SiC films that maybe effectively used in MEMS and NEMS devices. Silicon carbide filmshaving low residual stress, less than about 100 MPa, and preferably lessthan about 50 MPa, are highly desirable for MEMS and NEMS applications.Conventional deposition techniques have heretofore been unable toachieve such low stress values in polycrystalline silicon carbide films.

In these and other applications, control of stress properties, such asresidual stress and residual stress gradient, and electrical resistivityproperties also may be desired to achieve other preselected values thatmay not be low stress values.

These films are particularly suitable for use in devices operating inharsh environments because of the outstanding mechanical, electrical,and chemical properties of SiC. Examples of such applications includepressure sensors for internal combustion and jet engines, wind tunnelsensors and instrumentation, and instrumentation and control systems ofnuclear power systems. In addition, silicon carbide can be used indevice structures commonly made from silicon, such as accelerationsensors, biomedical sensors and actuators and other applications nottypically characterized by harsh environments. Silicon carbide can beused as an alternative material to silicon, capitalizing on the superiormechanical and chemical properties, as well as comparable electricalproperties between SiC and silicon.

Applicants have successfully produced thin polycrystalline SiC filmswith controlled properties on silicon and silicon dioxide substrates inwhich the residual tensile stress is at or near zero, the electricalresistivity is very low, and the residual tensile stress gradient isnear zero. These films were produced by a low pressure chemical vapordeposition process, using dicholorosilane (SiH₂Cl₂) as the precursor forsilicon (Si) and a mixture of 5% acetylene (C₂H₂) in hydrogen (H₂) asthe precursor for carbon. Applicants have determined that control of thesilicon precursor flow rate and/or the pressure at which the depositionoccurs allows for production of SiC film having the properties describedabove. Successful production of cantilevers, bridges, membranes, andlateral resonant structures has been completed, demonstrating theviability of the material fabricated in accordance with the presentinvention in micromachining applications.

It is believed that control of the flow rate of silicon precursor and/orthe deposition pressure of the reaction chamber while other parametersare fixed will enable control of the residual stress, the residualstress gradient, and the electrical resistivity of silicon carbide filmdeposited by vapor deposition for any silicon precursor and carbonprecursor. One of ordinary skill in art may determine the appropriatepressure and silicon precursor flow rate to achieve minimum residualstress, residual stress gradient, and electrical resistivity withoutundue experimentation, and use of alternate silicon and carbonprecursors does not depart from the spirit and scope of the invention.

Examples of possible alternate silicon precursors include silane,trichlorosilane, and tetrachlorosilane, among others. Possible alternatecarbon precursors include carbon-containing gases, methane, propane,ethylene, xylene, butane, carbon tetrabromide, and other hydrocarbons.

Possible alternate silicon and/or carbon precursors may includesingle-source precursors for both silicon and carbon. Examples ofpossible single-source precursors for both silane and carbon includehalosilane, trimethylsilane, tetramethylsilane, dimethyldimethoxysilane,tetramethylcyclotetrasiloxane, bis-trimethylsilylmethane,methyltrichlorosilane, tetraethylsilane, silacyclobutane, disilabutane,and any other material suitable for use as a single source precursor, ascan be determined by one of ordinary skill in the art.

If a single-source precursor is used, then either a separate carbonprecursor or silicon precursor may be provided to the chamber in orderto correctly control the ratio of carbon to silicon in the reactor. Inthis, event, the flow rate of the single source of the silicon or thesingle source of the carbon may be varied to achieve the proper ratio ofcarbon gas to silicon gas within the chamber so that the appropriatereaction occurs at the appropriate rate to deposit the silicon carbidefilm with the properties described above.

Other silicon-based films, such as silicon nitride (Si₃N₄), silicondioxide (SiO₂), silicon oxynitride (SiO_(x)N_(y)) and silicon carbonnitride (SiC_(x)N_(y)) may also be deposited with the method of thepresent invention using the appropriate precursors. In the case ofsilicon nitride, appropriate precursors may include silane (SiH₄) or DCSfor a silicon precursor, and ammonia (NH₃) for a nitrogen precursor. Thesilicon precursor flow rate or the deposition pressure may be varied toachieve a deposited film having the properties described above. Theoptimal range of deposition pressure and silicon precursor flow rate maybe determined without undue experimentation in accordance with thisinvention.

Other ceramic films based on a non-silicon ceramic may also be depositedwith the method of the present invention to achieve the propertiesdescribed above. Use of the term “ceramic” herein is defined asinorganic, nonmetallic materials, typically crystalline in nature (butcould be amorphous), and generally are compounds formed between metallicand nonmetallic elements, such as aluminum and oxygen (alumina—Al₂O₃),calcium and oxygen (calcia—CaO), silicon and oxygen (silica—SiO₂), andother analogous oxides, nitrides, borides, sulfides, and carbides. Theflow rate of the nonmetallic precursor is held fixed and the depositionpressure or the flow rate of the metallic precursor would be varied toachieve the properties described above. The optimal range of depositionpressure and metallic precursor flow rate may be determined withoutundue experimentation using the procedures provided herein.

Other compound semiconducting films based on materials other thansilicon may also be deposited with the method of the present inventionto achieve the properties described above. These materials include, butare not limited to, GaN, GaAs, InP, and other analogous semiconductormaterials deposited by chemical vapor deposition.

The examples described herein use silicon as the substrate material. Themethod described herein is not limited to use of silicon and siliconderivative substrates, such as silicon carbide and silicon dioxide, butrather can be applied to the deposition on any substrate material wherethe resultant film is subjected to a residual stress.

TEST PROCEDURE

FIGS. 1 and 2 illustrate the apparatuses used to conduct the followingprocedures. Prior to loading silicon substrate, wafers, of chips into areaction chamber 10, 110 of a low pressure vapor deposition apparatus12, 112, the wafers 14, 114 were cleaned using a standard RCA cleaningprocedure. Silicon wafers 14, 114 of 100 mm diameter were placed into aconventional hot-wall horizontal cylindrical quartz furnace 16, 116. Thereaction or deposition chamber 10, 110 was 2007 mm in length and 225 mmin diameter. The wafers were held in a SiC boat 18, 118 that rested on apaddle 20, 120 attached to a moveable front flange 22, 122 and placednear the center of the reaction chamber 10, 110.

In the configuration illustrated in FIG. 1, two small injection tubes24, one for the dicholorosilane and one for the acetylene, were used tointroduce these precursor gases into the chamber 10 directly underneaththe boat 18. To accommodate these injection tubes 24, the furnace tubewas of conventional design, consisting of a long, quartz cylinder 17that was capped on each end with metal flanges 22, 26. The injectiontubes 24 were attached to small ports on each of these flanges 22, 26.The front flange 22 consisted of a large circular plate that served asthe chamber door. This door was attached to a cantilever assembly forautomatic loading and unloading. The paddle 20 holding the SiC 18 boatwas attached only to the inside surface of the front flange doorassembly 22. The rear flange 26 was not movable and was equipped with anoutlet port that was attached to the vacuum system 28. Precursor gaseswere simultaneously introduced via the gas injection tubes 24 throughgas inlets 25 and ports in both the front flange 22 and the rear flange26.

In a second configuration illustrated in FIG. 2, the injector tubes 24were omitted. In this configuration, the furnace tube consisted of along quartz cylinder 117 that was circular in cross section at the frontend 130 and conical in shape at the rear 132. The front flange assembly122 was as described above and was affixed to the front end 130 of thecylinder. The rear 132 of the cylinder needed no flange, but insteadcontained a quartz nipple 134 that attached directly to the vacuumsystem 128. Gases were introduced into the chamber through gas inlets125 and ports in the front flange 122. No tooling was included to injectthe gases directly beneath the wafer boat 118.

The vacuum system 28, 128 consisted of a roots blower and mechanicalpump combination (not shown) that can reach a base pressure of less than1 mtorr in a fully loaded system, regardless of configuration. Pressurewas controlled through pressure control system 36, 136. A butterflyvalve 37, 137 was provided to assist with the pressure control. The gasflow rates and pressure control systems 36, 136 were controlled by aconventional furnace control computer system (not shown). Thetemperature in the reaction chamber 10, 110 was controlled via resistiveheating coils 38, 138.

Each load consisted of 25 Si wafers evenly distributed in a single,50-slot SiC boat. The first and last five wafers were designated asbaffling wafers to stabilize gas flow. Wafers in slots 6, 10, 13, 16,and 20 from the loading end were designated for study.

EXAMPLE 1

FIG. 1 illustrates the low pressure chemical vapor deposition apparatus12 used for these tests. Depositions were performed for two hours atpressure settings from about 0.42 torr to about 5 torr. In severalcases, longer times were used to deposit thicker films. The flow ratesof DCS and acetylene (5% in hydrogen) were held constant at about 54standard cubic centimeters per minute (sccm) and 180 sccm, respectively.The temperature was held fixed at about 900° C. The furnace wasconfigured with injector tubes to introduce the acetylene and DCS gasesinto the reaction chamber.

Following each deposition, the thickness of the films was measuredoptically using a Nanospec 4000 AFT spectrophotometer. The film residualstresses were determined by measuring the curvature of the siliconwafers before and after film deposition, using a laser-based curvaturemeasuring system (Frontier Semiconductor measurement, FSM 120). Siliconcarbide films were deposited on both sides of the wafer, and reactiveetching in a CHF₃/O₂ mixture was used to remove the film deposited onthe backside of the wafers.

FIG. 3 illustrates the relationship between the deposition pressure andthe residual tensile stress of the SiC at 900° C. resulting from thisseries of tests. The residual stress changed roughly from about 700 MPa(tensile) at 456 mtorr to about −100 MPa (compressive) at 5 torr, withfilms deposited at about 2.65 torr having near zero residual stress.Films deposited at pressures from about 2.5 torr to about 5 torr hadstress values between about 100 MPa and −100 MPa. The value of stressvaried little from wafer to wafer in the same run, as indicated by FIG.3.

Single layer cantilever beams were fabricated from about 500 nm-thickpolycrystalline SiC films made in accordance with this example tocharacterize the stress gradient at various deposition pressures. Thestress gradient is the change in the magnitude of residual stress as afunction of film thickness. Stress gradients can cause cantilever beamsto bend, whereas beams made from films with little or no stress gradientremain flat. For MEMS and NEMS devices, a stress gradient near zero isdesirable when the planarity of device structures is required. Aresidual stress gradient in the structural layers of MEMS/NEMS devicesis desirable in applications where curved or strained structures areneeded. In such structures, precise control of residual stress gradientis required. Control of stress gradients requires precision control ofresidual stresses.

FIG. 4( a) illustrates a cantilever beam 210 made in accordance with thepresent invention at about 2.65 torr. The beam 210 is generally flat andexhibits little, if any, bending. FIG. 4( b) illustrates a stressedcantilever beam 212 made in accordance with the present invention atabout 3.75 torr. This beam 212 bends slightly upward.

FIG. 5 illustrates the electrical resistivity of films made inaccordance with the present invention at various deposition pressures.These data indicate a relationship between deposition pressure andelectrical resistivity. The minimum electrical resistivity occurs nearthe deposition pressure at which the residual stress and the residualstress gradient are nearly zero, namely, about 2.65 torr. Electricalresistivity is less than 10 Ω·cm at deposition pressures from slightlygreater than about 2.0 torr to about 4.5 torr. While these values mayseem high relative to other semiconductors (including SiC), thesemeasurements were made from polycrystalline films that were not dopedeither before or after deposition. It is common practice to use dopingprocedures to reduce the electrical resistivity of semiconductingmaterials, especially SiC. These findings strongly suggest that dopingduring the deposition process will be most effective using conditionsthat favor low stress and low stress gradients.

EXAMPLE 2

The same procedure described above was used, except that the lowpressure chemical vapor deposition apparatus 112 illustrated in FIG. 2was used (no injectors, single front flange). For this series of tests,the deposition pressure was maintained essentially constant at about 2.0torr, and the flow rate of the silicon precursor, in this case DCS, wasvaried between about 18 sccm and about 54 sccm. The flow rate ofacetylene (5% in hydrogen) was fixed at about 180 sccm, and thetemperature of the reaction chamber was maintained at about 900° C.

As above, the films were characterized for residual stress, residualstress gradient, and electrical resistivity. FIG. 6 illustrates themeasured residual stress versus the flow rate of the DCS. The observedresidual stress decreased as a function of DCS flow rate until a flowrate of 36 sccm. The residual stress was substantially the same at aflow rate of 54 sccm as it was at a flow rate of 36 sccm. The residualstress as a function of flow rate, as illustrated in FIG. 6, appears tobe similar to the residual stress as a function of deposition pressure,as illustrated in FIG. 3.

FIG. 7 is a SEM micrograph of a micromachined second cantilever beam 214made in accordance with this example of the present invention at adicholorosilane flow rate of about 35 sccm. As seen from FIG. 6, adicholorosilane flow rate of about 35 sccm corresponds to residualstress of less than 50 MPa. Films with low residual stress values, suchas the second cantilever beam 214 in FIG. 7, exhibit very low residualstress gradient. The second cantilever beam 214 illustrated in FIG. 7exhibits substantially no bending.

FIG. 8 is a graph of electrical resistivity versus DCS flow rate,illustrating that the electrical resistivity exhibits a strongrelationship to DCS flow rate. The minimum value of electricalresistivity, slightly greater than 3 Ω·cm, occurs at 35 sccm and 36 sccmDCS. As with Example 1, the films were not intentionally doped eitherduring or after the deposition process. In this example, the electricalresistivity value and the residual stress nearest to zero occurred at aDCS flow rate of about 35 sccm.

While the present invention has been illustrated by the abovedescription of embodiments, and while the embodiments have beendescribed in some detail, it is not the intent of the applicants torestrict or in any way limit the scope of the invention to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art, such as the use of alternate precursors or thedeposition of alternate films. Therefore, the invention in its broaderaspects is not limited to the specific details, representative apparatusand methods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicants' general or inventive concept.

1. A process for achieving a predetermined value in a desired propertyselected from residual stress and electrical resistivity in a productceramic film deposited on a substrate by low pressure chemical vapordeposition, the ceramic being formed from a metallic element and anon-metallic element, the product ceramic film being formed by supplyinga metallic element precursor to a reaction chamber, separately supplyinga non-metallic element precursor different from the metallic elementprecursor to the reaction chamber under conditions of temperature andpressure such that the metallic element precursor and the non-metallicelement precursor react to form the product ceramic film on a substrateinside the reaction chamber, the process comprising (a) selectingpressure or flow rate of the metallic element precursor as the controlvariable, (b) determining the relationship between the desired propertyand the control variable when the remaining variables in the lowtemperature vapor deposition process are held at selected fixed values,and (c) during formation of the product ceramic film, achieving thepredetermined value for the desired property by controlling the controlvariable while maintaining the remaining variables at the above selectedfixed values.
 2. A process according to claim 1 for achieving a desiredresidual stress or electrical resistivity in a product silicon carbidefilm deposited on a substrate by low pressure chemical vapor deposition,the product silicon carbide film being formed by supplying a siliconprecursor to a reaction chamber, a separately supplying a carbonprecursor different from the silicon precursor to the reaction chamberunder conditions of temperature and pressure such that the siliconprecursor and the carbon precursor react to form the product siliconcarbide film on a substrate inside the reaction chamber, the processcomprising (a) selecting pressure or flow rote of the silicon precursoras the control variable, (b) determining the relationship betweenresidual stress or electrical resistivity and the control variable whenthe remaining variables in the low temperature vapor deposition processare held at selected fixed values, and (c) during formation of theproduct silicon carbide film, achieving the desired residual stress orelectrical resistivity by controlling the control variable whilemaintaining the remaining variables at the above selected fixed values.3. The method of claim 2, wherein the silicon precursor is selected fromthe group consisting of silane, halosilane, trimethylsilane,tetramethylsilane, dimethyldimethoxysilane,tetramethylcyclotetrasiloxane, bis-trimethylsilylmethane,methyltrichlorosilane, silane, tetraethylsilane, and silacyclobutane. 4.The method of claim 3, wherein the halosilane is selected from the groupconsisting of dichlorosilane, trichlorosilane, and tetrachlorosilane. 5.The method of claim 4, wherein the silicon precursor is dichlorosilane.6. The method of claim 2, wherein the flow rate of the carbon precursoris about 180 standard cubic centimeters per minute.
 7. The method ofclaim 2, wherein supplying carbon precursor comprises supplyingacetylene in hydrogen to the reaction chamber at a flow rate of about180 standard cubic centimeters per minute.
 8. The process or claim 2,wherein the product silicon carbide film is produced to have apredetermined electrical resistivity of about 10 Ω·cm or less.
 9. Theprocess of claim 8, wherein the predetermined electrical resistivity isachieved by controlling silicon precursor flow rate.
 10. The process ofclaim 9, wherein the silicon precursor flow rate is set to a valuebetween about 30 and 54 sccm to achieve the predetermined electricalresistivity.
 11. The process of claim 8, wherein the predeterminedelectrical resistivity is achieved by controlling pressure.
 12. Theprocess of claim 11, wherein pressure is set to a value between about0.42 torr and about 5 torr to achieve the predetermined electricalresistivity.
 13. The process of claim 2, wherein the product siliconcarbide film is produced to have a predetermined residual stress betweenabout 700 MPa to about and −100 MPa.
 14. The process of claim 13,wherein the predetermined residual stress is achieved by controllingpressure.
 15. The process of claim 14, wherein the pressure in thereaction chamber is set to a value between about 0.42 torr and about 5torr to achieve the predetermined residual stress.
 16. The process ofclaim 15, wherein the pressure in the reaction chamber is set to a valueof about 2 torr.
 17. The process of claim 13, wherein the predeterminedresidual stress is achieved by controlling silicon precursor flow rate.18. The process of claim 17, wherein the silicon precursor flow rate isset to a value between about 18 and 54 sccm to achieve the predeterminedresidual stress.
 19. A method of depositing a silicon carbide film on asubstrate by chemical vapor deposition, comprising (a) placing at leastone substrate in a reaction chamber; (b) maintaining the reactionchamber at a predetermined pressure; (c) supplying carbon precursor tothe reaction chamber at a predetermined fixed flow rate; (d) supplyingsilicon precursor to the reaction chamber at a flow rate; and (e)controlling the silicon precursor flow rate to control the stress in thedeposited silicon carbide film.